Hydraulic systems provide hydraulic fluid to hydraulic control devices to move and position members. The hydraulic systems can include a series of supply and return lines. One or more control devices are positioned along the supply and return lines and are attached to the members. A pump moves the hydraulic fluid through the supply and to the control devices. The hydraulic fluid from the control device is moved into the return line which returns the hydraulic fluid to the pump to be reused in the hydraulic system.
The members can have exterior forces exerted upon them during use. These exterior forces can cause unwanted movement of the members, which can include flutter. Flutter can be described as unstable aerodynamically-induced oscillations of the member. Unless damped, the oscillations can rapidly increase in amplitude with the potential for undesirable results, including exceeding the strength capability of the member and the control member. Contributing to the potential for flutter is elasticity in the hydraulic system. For example, hydraulic control devices can exhibit a linear spring response under load due to compressibility of the hydraulic fluid. The compressibility of the hydraulic fluid can be characterized by the cross-sectional area of the control device piston, the volume of the hydraulic fluid, and the effective bulk modulus of elasticity of the hydraulic fluid.
Methods of addressing flutter involve limiting the inertia of the load on the control device and/or increasing the size of the piston in the control device as a means to react the inertia load. Unfortunately, these methods result in a larger overall hydraulic system and/or larger control devices and/or are required to operate at higher hydraulic flow. The larger overall hydraulic system can include a larger physical size and/or increased weight.